Microstructure Estimates of Turbulent Salinity Flux and the Dissipation Spectrum of Salinity

Abstract

Direct determination of the irreversible turbulent flux of salinity in the ocean has not been possible because of the complexity of measuring salinity on the smallest scales over which it mixes. Presented is an analysis of turbulent salinity microstructure from measurements using a combined fast-conductivity/temperature probe on a slowly falling vertical microstructure profiler. Four hundred patches of ocean turbulence were selected for the analysis. Highly resolved spectra of salinity gradient ?Sz exhibit an approximate k+1 dependence in the viscous?convective subrange, followed by a roll-off in the viscous?diffusive subrange, as suggested by Batchelor, and permit the dissipation rate of salinity variance ?S to be determined. Estimates of irreversible salinity flux from measurements of the dissipation scales (from ?S, following Osborn and Cox) are compared to those from the correlation method (?w?S??), from TKE dissipation measurements (following Osborn), and to the turbulent heat flux. It is found that the ratio of haline to thermal turbulent diffusivities, dx = KS/KT = ?S/?T(dT/dS)2 is 0.6 < dx < 1.1.